Chocolate Streusel Muffins

Preheat oven to 425ºF. Line 12 muffin cups with liners.

For the streusel:
Stir flour, brown sugar, and cocoa. Add cubed butter and distribute through the mixture, using your fingers to mash the butter into smaller bits. Once the butter chunks are more like flat pellets and evenly dispersed, stir in chocolate chips. Set aside.

For the muffin batter:
In a large bowl, whisk flour, cocoa, baking powder, baking soda, and salt.

In a large measuring cup, whisk eggs lightly. Add sugar, chocolate milk and espresso powder, whisking until combined. Add extracts and then vinegar, and whisk again.

Pour wet ingredients, melted butter, and oil into the bowl with the dry ingredients. Stir until combined. Fold in chocolate chips.

Spoon batter into prepared tin. The liners will be full. Press a generous sprinkling of chocolate streusel onto each muffin. (Reserve any remaining streusel and refrigerate for another use.)

Bake for about 18 minutes, or until muffins bounce back when pressed in the center. Cool in pan for 5 minutes, then remove to a cooling rack. Serve warm or at room temperature.